Process for the recovery of oil

ABSTRACT

Heavy oil or crude oil spills in sea water are recovered without polluting environment. A natural rubber latex and a coagulant are scattered around lumps of oil spills to coagulate the latex with the coagulant, so that a membrane of the latex is formed around the oil lumps.

TECHNICAL FIELD

This invention relates to a process for the recovery of oil, forexample, recovery of heavy oil or crude oil spills on the sea caused byaccidents of tankers, recovery of oil deposits on rocks and seashores,recovery of oils leaked from oil tanks, and recovery and removal of oildeposits in tanks at the time of cleaning thereof.

BACKGROUND ART

Heavy oils or crude oils are occasionally discharged in sea water upontanker accidents. Heavy oils or crude oils are mixtures of aromatic oils(aroma oils), nephthene oils, paraffin oils, etc. and contain a largeamount of the aromatic oils. Because heavy oil or crude oil spills,which have a smaller specific gravity than sea water, initially afloaton a surface of the sea water in the form of lumps. Paraffin oils andnaphthene oils having a low viscosity are gradually separated bydiffusion from the lumps due to forces of waves or currents. Theremaining aromatic oils having a high density sink in the sea. Thus,part of the oil spills deposits on the seashores and oil deposits areadhered to rocks. It is, therefore, difficult to remove the oildeposits.

In addition to a manual method in which oils are collected with an oilfence and manually recovered, processes are known for treating oilspills in which the oils are decomposed with crude oil decomposingbacteria or the oils are mixed with sea water using an emulsifier. Theemulsifier and the crude oil decomposing bacteria used as a treatmentagent for this purpose serve to convert the oil into fine particleswhich are easily mixed with the sea water by emulsion and dispersion andto accelerate the spontaneous purification (destroy of oils such asthrough decomposition by bacteria, and oxidation and vaporization bysunlight). However, such spontaneous purification proceeds so slowlythat the known methods are not practical. Additionally, with thismethod, it is more and more difficult to recover the oil because, in anaccident of discharge of a large amount of oil, the oil treating agentdiffuses into and is diluted with a non-polluted region with time due towaves and currents. Thus, in practice, it is the general method tocollect the discharged oil manually.

Tanker accident is not the sole cause of discharge of heavy oils orcrude oils. Discard of waste oils from ships and discharge from oiltanks in harbors also cause such a problem. Similar to the removal ofoil deposits on rocks, cleaning of oil deposits on tanks brings about adifficulty.

It is, therefore, an object of the present invention to provide aprocess which can easily recover oil spills. Another object of thepresent invention is to provide a process which can recover such oilswhile minimizing environmental pollution. It is a further object of thepresent invention to provide a process which can easily remove andrecover oil deposits on solid surfaces.

DISCLOSURE OF INVENTION

The present invention is characterized in that a latex and a coagulantthereof are separately scattered on water containing an oil to diffusethe latex around the oil or in that the latex is coagulated by thecoagulant to form a coagulated latex membrane around the oil in thewater.

As the latex, there may be used a synthetic rubber latex and ahydrophilic polymer emulsion, such as polyvinyl acetate or polyvinylalcohol, in addition to a natural rubber latex. The latex is ahydrophilic colloid solution in which a highly polymerized compound isdispersed in water as a dispersing medium. It is preferred that thepolymer emulsion be prepared by emulsion polymerization for reasons thatthe product is in the form of an emulsion as such, though the presentinvention is not limited thereto.

The use of a natural rubber latex is most preferred. Such a latex is acolloid containing cis-1,4-isoprene polymer (about 54% by weight;concentration hereinafter is expressed in terms of % by weight), water(about 44%) and a protein (about 2%).

Any coagulant may be used as long as it can coagulate the latex. Forexample, polyvalent metal ions, polyvalent non-metal ions, organic acidsor alkali such as ammonia may be used.

The most preferable coagulant is a salt of Mg or Ca. Magnesium chlorideor calcium chloride is particularly preferable because these substancesare contained in the environment such as sea water and do not bringabout secondary pollution and because they are inexpensive.

The present invention is also characterized in that a lipophilic polymeremulsion gets in contact with oil deposits on solid surfaces such asrocks and tanks to solubilize the oils into the emulsion and in that theemulsion is thereafter coagulated to recover the oils.

The lipophilic polymer emulsion is an emulsion in which water of adiscontinuous phase is dispersed into an oil matrix phase. For example,there may be used an emulsion prepared by adding nonylphenol ether andpolyoxyethylene alkyl ether each in an amount of 0.2% to a naturalrubber latex to impart strong lipophilicity.

The latex, which is a hydrophilic colloid diffuses into the water, whenit is scattered around oil spills in sea water through a hose. Thescattered latex coagulates by reaction with the coagulant. Because thespecific gravity of the solids after the coagulation is smaller thanwater, a membrane is formed around the oil spills. The latexincorporated into lumps of oil spills does not coagulate as such.However, since water is generally present in the oil lumps, the latex isbrought into contact with an interface between the oil and water by theaction of waves and is thus coagulated.

The coagulated latex membrane is insoluble in oil but is compatibletherewith. Therefore, the latex is collected in the interface betweenthe oil spills and water and deposits on the interface of the oilspills. Since the coagulated latex membrane (hereinafter referred tosimply as latex membrane) is low in stickiness, oil spills can be easilyrecovered. Further, since the latex membrane is lighter than water, thearoma oils are prevented from sedimenting. The oil spills are surroundedby the latex membrane to prevent the dispersion of the oil lumps.

The oil lumps surrounded by the latex membrane have no stickiness and,thus, do not deposit on rocks and sand even when they arrive atseashores. Further, since the water temperature dependency of thecoagulation rate of the latex is small, oil spills can be recovered evenin winter season or in cold places.

When a natural rubber latex is used, unrecovered latex graduallydecomposes spontaneously and does not pollute the environment.

The present invention is mainly utilized for the recovery of oil spillsin sea water. Whilst magnesium chloride and calcium chloride to be acoagulant are originally present in sea water, the concentration thereofis so small that the coagulation rate of the latex is very slow. Thus,the scattered latex is unnecessarily diffused to reduce the efficiency.Therefore, it is necessary to scatter the coagulant.

The coagulant is scattered separately from the latex, for example, byusing separate hoses. However, the latex may be mixed with the coagulantin a scattering nozzle. The mixture is scattered at a scatteringpressure. In this case, for the purpose of preventing the coagulation ofthe latex by the coagulant within the nozzle, the concentration of thecoagulant is controlled to retard the coagulating power of thecoagulant. Alternately, this can be achieved by sufficiently reducingthe residence time of the mixture in the nozzle as compared with thetime required for the coagulation.

When a salt of Mg or Ca such as magnesium chloride or calcium chloride,which is originally contained in sea water, is used as the coagulant, noenvironmental pollution is caused.

The latex may be a mixture of a plurality of latices. When a syntheticlatex is used, it is advisable to add a decomposition enzyme, inparticular a decomposition enzyme for the emulsifier in the latex, sincethe unrecovered latex is decomposed so that a secondary pollution can beprevented.

A lipophilic polymer emulsion is used for oil deposits on rocks, etc. Insuch an emulsion, water forms discontinuous phase with the lipophilicsubstance forming a matrix phase. The oil deposits migrate into theemulsion. The emulsion is then gelled when coagulated with a coagulant.Thus, the oil can be removed from the rock, etc. and recovered.

The present invention can be applied not only to the recovery of crudeoils or heavy oils in the sea water but also to any utilization for therecovery of oil spills in water. Further, the present invention can beused not only for the removal and recovery of oil deposits on rocks butalso for the removal of oil deposits on, for example, walls of tanks.

In practicing the invention, the latex and the coagulant are scatteredfrom recovery ships, helicopters, etc. after crude oils, etc. aredischarged. For example, a tanker may be so constructed as to have adouble walled bottom structure and to store the latex and the coagulantseparately such that they are able to be discharged, if necessary,through valves. The thus stored latex and the coagulant are dischargedinto sea water when the tanker comes into a grounding accident and isbroken at the bottom thereof, so that the diffusion of the oil spillscan be prevented in situ.

The basic Japanese Patent Application No. H9-115217 filed on Apr. 16,1997 is hereby incorporated in its entirety by reference into thepresent application.

The present invention will become more fully understood from thedetailed description given hereinbelow. However, the detaileddescription and the specific embodiments are illustrative of desiredembodiments of the present invention and are described only for thepurpose of explanation. Various changes and modifications will beapparent to those ordinary skilled in the art on the basis of thedetailed description.

The applicant has no intention to give to public any disclosedembodiment. Among the disclosed changes and modifications, those whichmay not literally fall within the scope of the patent claims constitute,therefore, a part of the present invention in the sense of doctrine ofequivalents.

BEST MODE FOR CARRYING OUT THE INVENTION

Examples and experimental examples concerning the recovery of heavy oilswill be described hereinbelow but do not limit the invention thereto.

EXAMPLE 1

A stone (in a state where heavy oil deposited on the entire surface of astone of a weight about 10 kg) fouled as a result of an accident of oilspills from a Russian tanker “Nahotoka” in January, 1997 was collectedat the Sanriku seashore and was immersed for 2 seconds in a naturallatex of a polymer emulsion. The stone was separated from the emulsion.Then, the surface of the stone was strongly rubbed with a cloth. As aresult, a phenomenon was observed in which fine lumps of polymerparticles are formed. Thus, sticky layers of the fouling oil wereconverted into fine agglomerates surrounded by the latex and were ableto be easily removed. A brush was also used to easily remove oil in finerecesses. This was an application of unstabilization (flocculationphenomenon) of the latex from a stable state in which destroy of thestable state of the latex was accelerated by dynamic shearing forceswithout using a coagulant.

In this case, it is preferred that the natural latex be used inconjunction with an emulsifier for reasons that the oil removalefficiency is improved because the natural latex becomes lipophilic.

Experimental Example 1

C-Heavy oil (100 g) was placed on 2 liters of sea water in a 5 literglass vessel to form a sample. A natural rubber latex (10 cc; solidmatter content: about 56%) was added to the vessel from above. The latexwas dispersed into the whole sea water so that the sea water becamemilky white.

Subsequently, 20 g of bittern powder (major component: magnesiumchloride) was scattered, then the latex was gradually separated from thesea water and afloat with the C-heavy oil being surrounded therewith, sothat the sea water became transparent again after about 220 seconds.

The temperature of the sea water was about 10° C. throughout the aboveprocedure. When the sea water had a temperature of 0 C., it took about230 seconds until the sea water became transparent again. In the case of30° C., the time required was about 200 seconds. Thus, the temperaturedependency of the time required for forming a latex membrane around theC-heavy oil was low.

The C-heavy oil surrounded by the latex membrane had no stickiness andwas able to be easily recovered. Further, since the 100 g of the C-heavyoil was formed into one ball, the fluidity thereof was low. The latexmembrane of the ball surface was white and rubber-like. However, sincethe C-heavy oil located inside was able to see through the membrane, thewhole color tone was white-gray-grayish black in spots.

Experimental Example 2

Under the same conditions as above (water temperature: 10° C.), 100 g ofheavy oil recovered in the Noto Peninsula (light brown heavy oil spillsfrom a tanker recovered on the sea) was used in place of the C-heavyoil.

In the same manner as above, 10 cc of a natural rubber latex and 20 g ofbittern powder (major ingredient: magnesium chloride) were used. Whenthe latex was coagulated, a latex membrane was formed around therecovered oil. The sea water became transparent after about 220 seconds.

As a consequence of the coagulation of the latex membrane, a white-brownball was formed, in which the recovered oil was surrounded, and the ballwas free of stickiness and fluidity. Since the latex was also presentinside the ball, the hardness of the ball was higher than that inExperimental Example 1. This was because water was present inside theoil lump. The latex was thus dispersed in the water within the oil lump,so that the latex membrane was also formed inside the oil lump.

Experimental Example 3

The same sample as used in Experimental Example 2 was used, and 10 cc ofa synthetic rubber latex (SBR (styrene/butadiene rubber) latex;Nipol#4850 manufactured by Nippon Zeon Co., Ltd.) was used.

This latex had a solid matter content of 70% and was stabilized byadjusting the pH to about 11. As a coagulant, 20 g of a mixture of 50%of ZnO and 50% of Na₂SiF₆ were used. A latex membrane was formed aroundthe oil to form a ball. The sea water became transparent again after 75seconds. The time required for the sea water to become transparent bythe formation of a latex membrane is herein called “coagulation time”.

Experimental Example 4

The same sample as used in Experimental Example 2 was used, and 10 cc ofa synthetic rubber latex (isoprene latex; Kaliflex IR#700 manufacturedby Shell Chemical Co., Ltd.) was used.

This latex had a solid matter content of 65%. As a coagulant, 20 g of asolution of 60 g of calcium nitrate dissolved in 100 cc of methanol wasused. A latex membrane was formed around the oil to form a ball. The seawater became transparent again after 33 seconds.

Comparative Example 1

An experiment was performed under the same conditions (watertemperature: 10° C.) as those in Experimental Example 1 except that nocoagulant was used. In this case, the emulsion dispersed in the seawater remained milky state. The sea water did not return to atransparent state until a long time had passed. Thus, 5 days wererequired for the sea water to become transparent. In practice, thenon-coagulated emulsion will diffuse into sea water by waves andcurrents. No satisfactory results are obtained.

EXAMPLE 2

C-Heavy oil was applied on a rock to form an oil film. The oilfilm-bearing rock was allowed to stand out door for 2 days (temperature:0-10° C.). As a lipophilic emulsion, a mixed emulsion obtained byblending 100 parts by weight of a natural rubber latex, 2 parts byweight of nonylphenol ether and 2 parts by weight of polyoxyethylenealkyl ether, and then mixing the blend, with stirring, with 1.5 parts byweight of colloidal sulfur, 1.5 parts by weight of ZnO and 15 parts byweight of a spindle oil was used. The emulsion was applied onto the oilfilm with a brush.

Thereafter, an aqueous solution obtained by dissolving 20 parts byweight of Na₂SiF₆ and 15 parts by weight of sodiumdi-n-butyldithiocarbamate as a curing accelerator in 100 cc of warmwater was scattered over the surface of the emulsion. As a result of theapplication of the emulsion, the oil film was solubilized and dissolvedin the emulsion. The oil was coagulated by the coagulant to form a geland was able to be removed from the rock.

In the case where a silicate compound such as the above Na₂SiF₆ is usedas a coagulant, heating of the emulsion to about 50° C. with a hot windor a hot water is effective to accelerate the coagulation because thecoagulant is heat-sensitive. Thus, the coagulation proceeds morerapidly.

One preferred embodiment of the present invention is concerned with aprocess for recovering an oil, characterized by scattering a latex and acoagulant therefor over an oil-containing water, permitting the latex todiffuse around the oil in the water, and coagulating the latex with thecoagulant for forming a coagulated latex membrane around the oil for therecovery thereof.

In this case, the process for recovering an oil may be characterized inthat the latex is a natural rubber latex. Further, the process may becharacterized in that the coagulant is a salt of Mg or Ca and in thatthe oil is a heavy oil or crude oil in sea water.

Moreover, the process for recovering an oil may be characterized bycontacting an oil which deposits on a solid surface with a lipophilicpolymer emulsion to solubilize the oil in the emulsion and, then,coagulating the emulsion to recover the oil.

In the foregoing description, the coagulant is a substance that showsthe following function. Namely, the coagulant is a substance which canunstabilize a material which is homogeneously dispersed in a colloidalstate in water as an emulsion and which is in a stable state. Thus, thecoagulant is an unstabilizing agent and may be said as being a gellingagent or a flocculating agent.

The term “coagulation” is a phenomenon that a polymer in a latex isseparated from the serum, forming a lump, where the serum loses polymerto become transparent or the serum does not completely lose polymer theconcentration of which decreases. The polymer coagulated in this manneris referred to as coagulated substance or coagulum.

The term “gelation” is a phenomenon that a latex in a solution loses itsfluidity and is solidified as a whole in a gelatin-like state inconformity with the shape of a vessel. The product is called gel. Thegel thereafter shrinks so that a transparent serum is separated. Thisphenomenon is called syneresis.

The term “flocculation” is a phenomenon that fine agglomerates ofpolymer particles are formed in a large amount.

Chemicals which accelerate the destroy of a stable state of a normalemulsion such as a latex are herein referred to as coagulants orunstabilizing agents.

The concept of emulsion latex in the present invention will be describedhere. There are a variety of kinds of polymer emulsion latex. Variousclassifications are adopted therefor. As a rough classification, aclassification as shown in Table 1 is adopted on the basis of theproduction methods or procedures for the production. In the presentinvention, the emulsion latex is a general term of materials in which adispersed substance is a polymer and a dispersing medium is water orother liquids. Namely, the emulsion latex refers to a stable state of apolymer as a discontinuous phase with water or other liquid forming acontinuous phase.

Industrial Applicability

As having been described in the foregoing, according to a process forthe recovery of an oil of the present invention, it is possible toeasily recover, for example, heavy oil or crude oil spills on the seacaused by accidents of tankers, recover oil deposits on rocks andseashores, recover oils leaked from oil tanks, and recover and removeoil deposits in tanks at the time of cleaning thereof.

TABLE 1 Classification of Emulsion-Latex According to Kind of PolymerClassification of Classification of Composition and Abbre- Common Namein Polymer Short Name viation Japan Natural rubber NR Natural rubberlatex Styrene-butadiene Polybutadiene EBR EBR latex copolymer (styrenecontent: 0) Low styrene SBR SBR latex (styrene content: 5-40) Mediumstyrene SB SB latex (styrene content: 40-70) High styrene HS Highstyrene latex (styrene content: 70-95) Polystyrene PS Polystyrene latex(styrene content: 100) Acrylonitrile- Low nitrile NBR NBR latexbutadiene (A.N. content: copolymer 18-24) Medium nitrile (A.N. content:25-32) Medium high nitrile (A.N. content: 18-24) Methyl MBR MBR latexmethacrylate- (ABR) butadiene copolymer Polychloroprene CR Chloroprenelatex Vinylpyridine VP VP (vinylpyridine copolymer latexcis-1,4-Polyisoprene IR IR latex Butyl rubber IIR Butyl latexPolyvulcanized T Thiokole latex rubber Polyurethane U Urethane latexPolybutene PIB Polybutene emulsion Polyacrylate AR, AM Acrylate latex,Acryl emulsion Vinyl chloride PVC Vinyl chloride polymer (PVC) latexVinyl acetate PVAc Vinyl acetate latex polymer Vinylidene chloride PVdCVinylidene polymer chloride latex Polyethylene PE Polyethylene emulsionVinyl acetate EVA Ethylene vinyl ethylene copolymer acetate emulsion

Remarks: In addition to the above, there may be mentioned thosematerials which are obtained by copolymerizing trace components with theabove various polymers and which are named to have an affix such asmodified-, crosslinked, self-crosslinked- or carboxy-.

What is claimed is:
 1. A process for recovering an oil, comprising the steps of: scattering a natural rubber latex on sea water containing the oil, said natural rubber latex comprising a colloid containing, as main ingredients, cis-1,4-isoprene polymer and a protein; scattering bittern on said sea water; permitting said natural rubber latex to diffuse around the oil; and forming a membrane of said natural rubber latex around the oil.
 2. A process for recovering an oil as recited in claim 1, wherein the step of scattering the natural rubber latex comprises scattering the natural rubber latex on sea water containing heavy oil or crude oil.
 3. A process for recovering an oil as recited in claim 1, further comprising mixing said bittern with said natural rubber latex before the step of scattering said bittern and the step of scattering said natural rubber latex.
 4. A process for recovering an oil as recited in claim 2, further comprising mixing said bittern with said natural rubber latex before the step of scattering said bittern and the step of scattering said natural rubber latex.
 5. A process for recovering an oil as recited in claim 3, wherein the sten of mixing comprises mixing said bittern and said natural rubber latex such that a residence time of a mixture of said bittern and said natural rubber latex is shorter than a time required for a coagulation of said natural rubber latex caused by said bittern.
 6. A process for recovering an oil as recited in claim 4, wherein the step of mixing comprises mixing said bittern and said natural rubber latex such that a residence time of a mixture of said bittern and said natural rubber latex is shorter than a time required for a coagulation of said natural rubber latex caused by said bittern.
 7. A process for recovering an oil as recited in claim 1, wherein the step of scattering the natural rubber latex comprises scattering a natural rubber latex comprising a colloid containing 54% by weight cis-1,4-isoprene polymer, 2% by weight protein and 44% water.
 8. A process for recovering an oil, comprising the steps of: contacting an oil, which coexists with sea water on a solid surface, with a natural rubber latex and a bittern, said natural rubber latex being a colloid containing, as main ingredients, cis-1,4-isoprene polymer and a protein; covering the oil with said natural rubber latex; and coagulating said natural rubber latex. 